Résumé
Plant-bacterial interactions in the rhizosphere are important in mediating soil nutrient transformations. Plants supply carbon-rich substrates to rhizobacteria as root exudates and bacteria mobilise soil-bound phosphate for plant nutrition. This study aimed to probe the specificity of the plant effect on bacterial gene expression in P-starved rhizosphere conditions.
DNA microarrays were employed to study gene expression in the rhizosphere of Lolium perenne grown under high and low phosphate regimes (330 mu M vs. 3-6 mu M phosphate). Root exudation under these regimes was also quantified. Phosphate-regulated gene expression of a panel of 22 genes was compared in rhizosphere, planktonic culture and during biofilm growth on an artificial root.
Plant growth and root exudation were affected by P-availability. P-limited conditions induced increased expression of bacterial genes of an aromatic degradation pathway (catA), heavy metal sensing (PA2523), and membrane proteins (glpM, crcB), while genes involved in cell motility and amino acid uptake/ metabolism were downregulated. A crcB mutant was impaired in rhizosphere survival under low phosphate conditions, though glpM and catA mutants were not affected. Several of the genes studied were induced by phosphate limitation in all three lifestyles studied.
Our results show the importance of the plant-microbe interaction in controlling the bacterial transcriptional response in a phosphate-limited rhizosphere.